Posted by
Ryan on
Dec 30, 2009; 1:46pm
URL: http://spssx-discussion.165.s1.nabble.com/cronbach-alpha-for-binary-responses-tp1086058p1086072.html
Eins,
Instead of restating what was said succintly already by a poster in another group addressing a very similar question, I'll provide you with the link below.
--
http://groups.google.com/group/sci.stat.consult/browse_thread/thread/61eff485b422a0d2/8e6838b85c1a9b7f?hl=en&lnk=gst&q=cronbach%27s+dichotomous+#8e6838b85c1a9b7f--
If for some reason the link above does not work, I've reproduced the response in quotes below:
"It depends on what you expect alpha to tell you. If you're looking
for confirmation that all the items are "measuring the same thing"
then forget alpha -- you want to factor the items, and you should
probably do it using tetrachoric correlations. A high alpha does
not imply that there is only one factor, and a low alpha does not
imply that there are many factors.
The proper use of alpha is as a quick and dirty estimate of a
lower bound for the reliability of the total score. (If you're
not computing a total score then you don't care about alpha.)
The interpretation is asymmetric: a high alpha means a high
reliability, but a low alpha does not mean a low reliability.
Alpha is a function of only two things: the number of items,
and the average correlation among them. An easy way to remember
this is alpha/(1 - alpha) = k * rbar/(1 - rbar),
where k = the number of items, and
rbar = (average item-item covariance)/(average item variance),
which is a kind of weighted average item-item correlation. "
--
Ryan
eins wrote
May I know if Cronbach alpha can be used as measure of reliability for a correct/wrong response (coded 0 or 1) items? I want to use it for each subscale (with 8 items each) of my instrument with three scales. Thank you for your comments.
Eins
Design your own exclusive Pingbox today! It's easy to create your personal chat space on your blogs.
http://ph.messenger.yahoo.com/pingbox